Utility lines for water, electricity, gas, telephone and cable television are often run underground for reasons of safety and aesthetics. In many situations, the underground utilities can be buried in a trench which is then back-filled. Although useful in areas of new construction, the burial of utilities in a trench has certain disadvantages. In areas supporting existing construction, a trench can cause serious disturbance to structures or roadways. Further, there is a high probability that digging a trench may damage previously buried utilities, and that structures or roadways disturbed by digging the trench are rarely restored to their original condition. Also, the trench poses a danger of injury to workers and passersby.
The general technique of boring a horizontal underground hole has recently been developed in order to overcome the disadvantages described above, as well as others unaddressed when employing conventional trenching techniques. In accordance with such a general horizontal boring technique, also known as microtunnelling or trenchless underground boring, a boring system is positioned on the ground surface and drills a hole into the ground at an oblique angle with respect to the ground surface. Water is flowed through the drill string, over the boring tool, and back up the borehole in order to remove cuttings and dirt. After the boring tool reaches the desired depth, the tool is then directed along a substantially horizontal path to create a horizontal borehole. After the desired length of borehole has been obtained, the tool is then directed upwards to break through to the surface. A reamer is then attached to the drill string which is pulled back through the borehole, thus reaming out the borehole to a larger diameter. It is common to attach a utility line or conduit to the reaming tool so that it is dragged through the borehole along with the reamer.
At the commencement of an underground boring operation, the boring tool is typically rotated and advanced into the ground. As the boring tool progresses underground, the tool typically encounters soil of varying hardness. When the boring tool encounters relatively hard ground, the rate of tool rotation can decrease significantly. An increase in torque is typically imparted to the boring tool through manual manipulation of appropriate control levers in order to continue advancing the tool through the harder ground. Such an increase in torque, however, must be moderated carefully by the operator in order to avoid damaging the boring tool or other system components.
An operator of a conventional underground boring tool typically modifies the rate of boring tool advancement when the tool encounters hard soil by manipulating one or more control levers and monitoring various analog gauges. As can be appreciated, a high degree of skill and continuous attention are required on the part of the operator in order to operate the boring tool productively and safely. Maintaining optimum boring machine performance using prior art control methods is generally considered to be an exacting and fatiguing task. In addition, although a skilled operator may react quickly to dynamically changing boring conditions, human reaction time to such changes is rather slow.
There is a recognition among manufacturers of underground boring machines for a need to minimize the difficulty of operating a boring machine. There exists a further need to reduce the substantial amount of time currently required to adequately train an underground boring machine operator. Additionally, there continues a need for an improved underground boring machine that provides for high boring efficiency through varying ground conditions without depending on human intervention. The present invention fulfills these needs.